Changing family of many metas
According to the wiki the family of a meta is defined by its name. Since the names of objects in Blender are automatically generated when duplicating them I don't think it is possible to copy metas into a new family.

There might however be a workaround for what you are trying to do: Select all your metas and copy them to a buffer by pressing [Ctrl+C]. Then convert the metas to a mesh. If you now press [Ctrl+V] the previous metas will be pasted from the buffer and you have your mesh and your metas.